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Abstract:

The present invention relates to compositions and use of fluidized polymer
suspensions containing allyloxy linkage and its functional derivatives,
and water soluble polymers for use in oil field applications as fluid
additives for drilling and cementing processes.

Claims:

1. An aqueous fluidized polymer suspension for use in oilfield
applications, comprising:an allyloxy based co-polymer;a water soluble
polymer;a salt; andwater;wherein the water soluble polymer is selected
from the group consisting of hydroxyethylcellulose (HEC),
carboxymethylcellulose (CMC), guar, guar derivatives and xanthan.

10. An oil-well servicing fluid comprising:a. an aqueous fluidized polymer
suspension; andb. a particulate componentwherein the aqueous fluidized
polymer suspension further comprises an allyloxy based co-polymer, a
salt, water, and a water soluble polymer selected from the group
consisting of hydroxyethylcellulose (HEC), carboxymethylcellulose (CMC),
guar, guar derivatives and xanthan.

Description:

[0001]This application claims the benefit of U.S. Provisional Application
Ser. No. 60/932,425, filed on May 31, 2007, which is incorporated herein
by reference in its entirety.

FIELD OF THE INVENTION

[0002]The present invention relates to a composition and use application
of water-soluble polymers and co-polymers for oil-well servicing fluids,
such as cementing or drilling applications. Specifically, the present
invention relates a mixture of a synthetic polymer containing allyloxy
linkage and its functional derivatives and hydroxyethyl cellulose and for
its use in oil field applications as a fluid loss additive for drilling
fluids and cementing slurries. More specifically, a pumpable liquid
product comprising a mixture of a synthetic polymer containing allyloxy
linkage and its functional derivatives and hydroxyethyl cellulose.

BACKGROUND FOR THE INVENTION

[0003]Polymers are used extensively in oil field application as fluid
additives for drilling, cementing, gas and oil well fracturing and
enhanced-oil-recovery processes. Synthetic, organic, and inorganic
polymers, as well as cellulose ethers and guar gum and guar derivatives,
are widely used in oil field applications. These materials are also
applied in a variety of formation-damage control applications and as
dispersing agents.

[0004]In the initial drilling operation of an oil or gas well, a drilling
fluid, commonly referred as "drilling mud," is pumped under pressure down
to a string of drill pipes through the center of the drilling bit, back
through the space or annulus between the outside of the drilling stem and
the borehole wall, and finally back to the surface. After a well has been
drilled and oil discovered, one or more subterranean,
hydrocarbon-producing formations are most often encountered. The well is
then completed to obtain the maximum hydrocarbon production from the
subterranean producing formations.

[0005]Completion of a well refers to the operations performed during the
period from drilling-in the pay zone until the time the well is put into
production. These operations may include additional drilling-in,
placement of downhole hardware, perforation, sand control operations,
such as gravel packing, and cleaning out downhole debris. A completion
fluid is often defined as a wellbore fluid used to facilitate such
operations. The completion fluid's primary function is to control the
pressure of the formation fluid by virtue of its specific gravity. The
type of operation performed, the bottom hole conditions, and the nature
of the formation will dictate other properties, such as viscosity. Use of
completion fluids also clean out the drilled borehole. Oil well cement
compositions are used in the completion operation to make a permanent,
leak proof well for continuous use.

[0006]In cementing operations of gas or oil wells, hydraulic cement is
normally mixed with sufficient water to form a pumpable slurry and the
slurry is injected into a subterranean zone to be cemented. After
placement in the zone, the cement slurry sets into a hard mass. In
primary cementing, where cement slurry is placed in the annulus between a
casing or liner and the adjacent earth formations, loss of fluid is a
major concern. The formations can result in premature gelation of the
cement slurry and bridging of the annulus before proper placement of the
slurry. In remedial cementing operations, the control of fluid loss is
necessary to achieve the more precise cement slurry placement associated
with such operations.

[0007]Among all other slurry properties, fluid loss control is one of the
critical concerns for cement slurry formulation, especially at high
temperature, high pressure (squeeze cement) and salt environments. The
main purpose of fluid loss additives is to prevent the dehydration of the
cement slurry that can reduce its pumpability as well as affecting its
other designed properties. Loss of a significant amount of water from the
cement slurry can cause changes in several important job parameters, such
as reduced pumping time and increased frictional pressure. Fluid loss
additives are used to help prevent water loss from cement slurries to the
rock formation as the slurry is pumped into the annulus between the
casing and the well bore. This allows displacing the maximum amount of
mud, compressive strength development, and bonding between the formation
and the casing. In fact, under harsh conditions and due to permeable
zones, the slurry can dehydrate quickly and become unpumpable, preventing
the extension of slurry into voids and channels, particularly where the
annular space between the liner and the open hole is too narrow. Any
bridging problem due to high fluid loss would considerably disturb the
cement job and affect the integrity of the cement column.

[0008]A large variety of synthetic polymeric fluid loss additives have
been used in drilling fluid and oil-well cement slurries. These synthetic
polymeric fluid loss additives are mainly used for high temperature
operations. Among many other mechanisms of action, it is well known that
the fluid loss control efficiency is greatly affected by the molecular
weight of the polymeric additive. However, for cement slurries, high Mw
polymers (>1,000,000 Daltons) exhibit an undesirable side effect
related to a viscosity increase of the slurry. Low Mw versions
(<1,000,000 Daltons) are useful to prevent the viscosity side effect,
but the slurry stability could be affected by cement settling and free
water due to lack of suspending capacity of those polymers. It has been
found that by using a selected hydroxyethyl cellulose in combination with
a low Mw synthetic polymer, a pumpable liquid product that is effective
in fluid loss control without a free water problem can be obtained.

[0009]Previously, it was not possible to prepare a liquid mixture of these
two polymers that has a viscosity low enough to be pumpable. In fact,
hydroxyethyl cellulose has a tendency to dissolve in the mixture,
resulting in a gel like solution.

[0010]U.S. Pat. No. 4,883,536 describes suspensions of
hydroxyethylcellulose prepared in concentrated aqueous solutions of
diammonium sulfate or diammonium phosphate, and that these suspensions in
turn were useful for rheology modification of latex paint. U.S. Pat. No.
5,228,908 describes that concentrated aqueous sodium formate solution can
be employed for preparation of fluid suspensions of the polymers such as
hydroxyethylcellulose as well. In U.S. Pat. No. 5,578,168, the use of a
number of salts, including sodium formate, were shown to be useful for
preparing aqueous suspensions of poly(ethylene oxide). In U.S. Pat. Nos.
5,541,241 and 5,489,638, it was demonstrated that sodium formate and
other salts were useful for preparing aqueous suspensions of polyvinyl
alcohol.

BRIEF DESCRIPTION OF THE INVENTION

[0011]The present invention is directed to an aqueous fluidized polymer
suspension for use in various oilfield applications, particularly in
cementing and drilling applications containing an allyloxy based
co-polymer, a water soluble polymer; a salt; and an amount of water. The
water soluble polymers of use in the present invention may be selected
from the group consisting of hydroxyethylcellulose (HEC),
carboxymethylcellulose (CMC), guar, guar derivatives and xanthan.

[0012]The present invention also relates to an oil-well servicing fluid
comprising the aqueous fluidized polymer suspension; and a particulate
component such as cement, silica flour, fumed silica, pozzoline, sodium
silicate, calcium carbonate, barite, hematite and clay. The oil-well
servicing fluid in certain embodiments may function as a cement slurry or
in other embodiments may find utility as a drilling fluid.

DETAILED DESCRIPTION OF THE INVENTION

[0013]The present invention relates to a pumpable and stable mixture
composition of a water soluble polymer with allyloxy based co-polymers,
more fully described in U.S. Pat. No. 6,465,587 incorporated herein by
reference in its entirety. The water soluble polymer is selected from the
group consisting of hydroxyethylcellulose (HEC), carboxymethylcellulose
(CMC), guar, guar derivatives and xanthan. A preferred water soluble
polymer is HEC. The guar derivatives of use in the present invention
include hydroxypropyl guar, carboxymethyl guar, and carboxymethyl
hydroxypropyl guar.

[0014]These allyloxy based co-polymers contain allyloxy linkage and its
functional derivatives as oil field fluid loss additives in drilling
operations. Specifically, co-polymers containing acrylamide, and
3-allyloxypropanesulfonate ("AHPS") and other monomers are synthesized.
The AHPS component of the co-polymers is thermally and hydrolytically
stable at high pH, saturated salt and elevated temperature conditions.

[0015]One component of the copolymer of use in the present invention
comprises monomeric repeat unit(s) of alpha, beta ethylenically
unsaturated compound of Formula (I),

-(E)- Formula (I)

wherein "E" is the repeat unit obtained after polymerization of an alpha,
beta ethylenically unsaturated compound, preferably a carboxylic acid, an
amide form of the carboxylic acid, and a lower alkyl(C1-C6) ester or
hydroxylated lower alkyl(C1-C6) ester of such carboxylic acid. Compounds
from which "E" may be derived include the acrylic acid, methacrylic acid,
acrylamide, maleic acid or anhydride, itaconic acid, crontonic acid,
fumaric acid, styrene, styrene sulfonate, vinyl pyrrolidone,
N-methylacrylamide, N-isopropylacrylamide, N-butylacrylamide,
N,N-dimethylacrylamide, N-hydroxymethylacrylamide,
N-hydroxymethylacrylamide and other N-alkylacrylamides. Water-soluble
salt forms of the carboxylic acids are also of use in the copolymer of
use in the present invention.

[0016]Another component of the copolymers is the repeat unit formed by the
polymerization of a monomer containing sulfonate functionality as shown
in Formula (II),

wherein R1 is hydrogen or a lower alkyl(C1 to C5), R2 and
R3 are identical or different and denote hydrogen, or C1 to
C5 alkyl groups; and, M is hydrogen or a water-soluble cation (e.g.,
NH4.sup.+, alkali metal). 2-Acrylamido-2-methylpropanesulfonic acid
(AMPSR) is a typical example of a Formula (II) monomer. However,
compounds such as styrene sulfonate, vinyl sulfonate and allyl sulfonate
also fall in the category.

[0017]A third component of the copolymer is the repeat unit formed by the
polymerization of a substituted allyl alkylene ether compound as shown in
Formula (III),

wherein R1 is hydrogen or lower alkyl(C1-C5), R4 is a hydroxyl
substituted alkylene group having from 1 to about 6 carbon atoms or a
non-substituted alkyl or alkylene group having from 1 to about 6 carbon
atoms; X is an anionic radical (e.g., sulfonate, phosphate, phosphite or
phosphonate); and, Z is one or more hydrogen or a water soluble cation or
cations which together counterbalance the charge of X. Compounds
encompassed by Formula (III) include the repeat unit obtained after
polymerization of 3-allyloxyhydroxypropanesulfonate,
3-allyloxyhydroxypropanesphosphite, and
3-allyloxyhydroxypropanesphosphate.

[0018]It is noted that more than one monomer unit in Formula I, II and III
mentioned above may be present in the copolymers of use in the present
invention. Therefore, the polymer of use in the present invention is
comprised of copolymer, terpolymer and tetrapolymer or more wherein two,
three, four or more different monomeric repeat units selected from the
repeat units described in Formulas I, II, and III are present in the
polymer. There is no limit to the kind and mole percent of the monomers
chosen so long as the total mole percent adds up to 100 mole % and the
resulting copolymers are water soluble or water dispersible.

[0019]Branching or cross-linking agents such as
methylenebis(meth)acrylamide, polyethyleneglycol di(meth)acrylate,
hydroxyacrylamide, allyl glycidyl ether, glycidyl acrylate and the like
may also be added for the copolymers.

[0020]A particular allyloxy based co-polymer used in the various examples
of the present invention is available from Hercules Incorporated as
XxtraDura® FLA 3766 universal fluid loss additive for cementing.
Amongst the objectives of the present invention is to combine a water
soluble polymer which is functioning as a free water control agent, with
a relatively low Mw synthetic co-polymer, such as an allyloxy based
co-polymer to improve free water control properties and ultimately
stability of oil-well servicing fluids in general and cement slurry
compositions in particular.

[0021]By applying aqueous fluidized polymer suspensions (FPS) technology,
as generally taught in U.S. Pat. Nos. 4,883,536 and 5,228,908
incorporated herein by reference in their entireties, to a mixture of
water soluble polymer and allyloxy based co-polymer, it was found that
low viscosity/pumpable aqueous mixtures of water soluble polymer and an
allyloxy based co-polymer containing a small amount of selected salts
could be prepared at polymer solids content over 15%.

[0023]The salts are used in the FPS of the present invention in
concentrations is in a range of about 2 wt % to less than about 30 wt %,
preferably in the range of about 5 wt % to 10 wt %, of the aqueous
fluidized polymer suspension.

[0024]The use of the aqueous FPS technology results in a stable, pourable
fluid suspension containing high concentrations of water-soluble
polymers.

[0025]Suspension", "dispersion", "solution" and other terms are often
confused. Thus, it should be understood that herein "suspension" and
"dispersion" are used interchangeably to mean a system in which solid
particles (water-soluble polymer) are dispersed in a liquid (water). It
should also be understood that "solution" means a homogenous mixture of a
solvent (e.g., water) with a solute (e.g., dissolved salt, dissolved
water-soluble polymer, etc.).

[0026]The aqueous fluidized polymer suspension of the present invention is
useful in producing various oil-well servicing fluids. The oil-well
servicing fluids comprise the aqueous fluidized polymer suspension as
well as a particulate component useful as cements, drilling fluids, etc.
The particulate component may be any of the numerous particulate
materials used in oil-well servicing fluids and selected from the group
consisting of cement, silica flour, fumed silica, pozzoline, sodium
silicate, calcium carbonate, barite, hematite and clay. A preferred
particulate component is cement.

[0027]The invention will now be further described with reference to a
number of specific examples which are to be regarded solely as
illustrative, and not as restricting the scope of the invention.

EXAMPLES

Examples 1-12

Aqueous Fluidized Polymer Suspensions

[0028]Examples 1-12 are examples of various aqueous fluidized polymer
suspensions are set forth in the following tables. All amounts are by
weight, unless otherwise indicated.

[0029]The viscosity of the aqueous fluidized polymer suspensions of the
present invention were determined using a Brookfield viscometer with a
number 3 spindle and at 30 revolutions per minute. The viscosities are
listed in centipoise cPs.

[0030]The aqueous fluidized polymer suspensions were made according to the
teachings set forth in U.S. Pat. Nos. 4,883,536 and 5,228,908 where the
salt is first added to the water and dissolved to produce an aqueous
solution. Subsequently, the allyloxy based co-polymer and the water
soluble polymer used in the suspension are added to the aqueous solution
and mixed to produce the aqueous fluidized polymer suspensions of the
present invention.

[0031]The above described aqueous fluidized polymer suspensions all
appeared generally to be of utility in subsequent use in cement
formulations.

Examples 13-21

Cement Formulations

[0032]Examples 13-21 are examples of cement formulations produced using
various aqueous fluidized polymer suspensions examples as described above
in order to demonstrate the performance of the aqueous fluidized polymer
suspensions of the present invention in cementing applications. These
cement formulations were tested at various temperatures for Fann Rheology
as well as the amount of filtrate collected.

[0033]The rheology of the slurry was then measured with a FANN 35
viscometer at room temperature.

[0034]The performance testing of the oil well cement formulations were
conducted in terms of rheology and fluid loss properties at variable
bottom hole cement temperatures ("BHCT"). Typically, the rheology was
measured just after the slurry preparation at room temperature (about
26.7° C., 80° F.), to simulate the mixing and pumping at
the surface, and after conditioning the slurry under BHCT (about
82.2° C., 180° F.) for 20 minutes as recommended by the
American Petroleum Institute ("API"). The fluid loss properties were
measured at BHCT temperature after the formulations conditioning.

[0035]To simulate downhole circulating conditions, the cement formulations
was then left for conditioning at the test temperature (BHCT) for 20
minutes. In the mean time, a high pressure/high temperature ("HPHT")
fluid loss cell was pre-heated at the required test temperature.

[0036]After conditioning the cement formulations, the rheology was
measured again at the test temperature as above as well as the fluid loss
properties. The fluid loss properties are expressed as API fluid loss
when the volume collected corresponds to the filtrate collected after 30
minutes testing or as calculated fluid loss when the test blows out
before the test reaches 30 minutes.

[0037]Experiments demonstrate that concentrations of salt in the range of
about 5 wt % to 10 wt % are sufficient to prepare suspensions with water
soluble polymer content in the range of about 1 wt % to 20 wt % of the
aqueous fluidized polymer suspension. The resulting mixture viscosity was
considered pumpable and was in the range of 280 cPs to 3200 cPs,
depending upon the type and concentration of the water soluble polymer
used as a free water agent (Natrosol®) 210 HHX hydroxyethylcellulose,
Natrosol® 250H4BXR hydroxyethylcellulose, and Natrosol® 250
HHBR hydroxyethylcellulose all available from Hercules Incorporated) as
well as guar, including depolymerized guar. The mixtures were observed to
be stable for over one (1) week.

[0038]Application data run with the HEC/allyloxy based co-polymer and
depolymerized guar mixtures demonstrated a clear difference in term of
rheology as compared to allyloxy based co-polymer used as a single
component without sacrificing the fluid loss control properties. The
rheology was much higher, and no free water was observed while the fluid
loss remains in same order of magnitude.

[0039]The above application data indicates that easily pumpable and stable
mixtures of water soluble polymers, such as hydroxyethylcellulose (HEC),
carboxymethylcellulose (CMC), guar, guar derivatives and xanthan, and an
allyloxy based co-polymer, were prepared using fluidized polymer
suspension technology. The resulting mixtures would have utility in
various oilfield applications, particularly in cementing and drilling
applications.

[0040]While this invention has been described with respect to particular
embodiments thereof, it is apparent that numerous other forms and
modifications will be obvious from this disclosure to those skilled in
the art. The appended claims and this invention generally should be
construed to cover all such obvious forms and modifications which are
within the true spirit and scope of the present invention.